(a) Field of the Invention:
The present invention relates to a magnetic disc drive system having a liquid bearing and, more particularly, to a magnetic disc drive system, having a liquid-bearing for a magnetic head slider, for use in a computer system.
(b) Description of Related Art:
Recently, the recording densities of various information storage drives have steadily increased. In a magnetic disc drive system, one important factor in increasing the recording density thereof is to decrease the spacing between a recording disc and a read/write magnetic head for reading and/or writing information stored on the recording disc.
To decrease the spacing, magnetic disc drive systems utilizing a liquid bearing in place of an air bearing have been proposed, for example, in patent publications JP-A-4(1992)-113568, U.S. Pat. No. 2,969,435, U.S. Pat. No. 3,005,675, U.S. Pat. No. 3,579,212, U.S. Pat. No. 4,633,351, and U.S. Pat. No. 5,202,803. In a magnetic disc drive system of this type, a magnetic head slider bears on a liquid bearing film to provide a spacing between a recording medium and a magnetic head, the spacing being substantially equal to the thickness of the liquid bearing film.
The thickness of such liquid bearing film is as low as about 20 nanometers (nm) and the surface roughness of the magnetic disc or the magnetic head slider can only be decreased down to a few nanometers, which is still one fifth the spacing. For this reason, the magnetic head slider cannot follow the magnetic disc well when the slider is moved at a linear speed greater than 10 m/sec relative to the magnetic disc. That is, it is difficult to prevent the magnetic head slider from jumping. In the disc drives disclosed in the Japanese and U.S. patent publications mentioned above, perfluoropolyethers having no polar functional groups, such as GALDEN D02 of Montefluos Co. and KRYTOX of Du Pont Co., are used.
Since such non-polar perfluoropolyethers do not provide sufficient interaction with the magnetic head slider or magnetic disc, jumping of the magnetic head slider cannot be prevented even when such non-polar perfluoropolyethers are used.
U.S. Pat. No. 5,202,803 discloses a perfluoropolyether having a single polar group made of DEMNUM SP of Daikin Industries, Ltd. and a hydrocarbon having a double bond such as POLY-1-DECENCE, both used for forming a liquid bearing.
Even when such liquids are used, jumping of the magnetic head slider cannot be avoided, because those liquids only have weak interaction with the magnetic head slider or the magnetic disc.
As is disclosed in patent publication No. JP-A-5(1993)-54578, it has been proposed to utilize the surface tension of a liquid lubricant layer and the pressure of the liquid lubricant formed on the uppermost layer of a magnetic disc to prevent the magnetic head and magnetic disc from contacting and to each other, and to thereby avoid breakage thereof and decrease the spacing therebetween.
In the disc drive disclosed in JP-A-5-54578, a perfluoropolyether having a polar terminal group is used for forming a liquid bearing, whereby the spacing between the magnetic head and the magnetic disc is maintained constant by the attractive force produced due to the surface tension and pressure of the liquid bearing.
In the case of a spherical slider having a radius of curvature (R) as disclosed in JP-A-5-54578, attractive force (F) due to surface tension (y) can be expressed by the following equation (1): EQU F=4.pi.R.multidot.y. (1)
Equation (1) is shown in "Friction and Lubrication of Solid", presented by Bauden Teiber, p 285, 1961. As is apparent from equation (1), the attractive force (F) does not depend on the spacing (h).
That is, the attractive force (F) due to surface tension (.gamma.) is not expressed as a function of spacing (h), so that the attractive force (F) does not produce the effect of preventing the spacing (h) from increasing, i.e., preventing jumping of the magnetic head slider. Moreover, the surface tension of a perfluoropolyether having a polar terminal group is small, and therefore insufficient to avoid jumping of the magnetic head slider.
Even when a non-polar perfluoropolyether such as GALDEN D02 or KRYTOX is used, only a small surface tension can be obtained. This is a common problem in using organic materials containing fluorine.
Contact type magnetic disc drives have been proposed in which the dimensions of the magnetic head slider and supporting member for supporting the magnetic head slider are decreased so as to reduce their weights, for example, in "Journal of the Magnetic of Japan", Vol. 15, Supplement No. S2 (1991), 483 presented by H. Hamilton and patent publication JP-A-5-508808.
In conventional air bearings, it has been proposed that two to four bearing surface pads be provided on the bearing surface of the magnetic head slider in order to obtain an air bearing.
JP-A-6-36486 discloses a magnetic head slider having two bearing surface pads arranged in the transverse direction of an air bearing surface. JP-A-6-52645 discloses a magnetic head slider having two bearing surface pads (leading pad) disposed near the leading side of the air bearing surface of the magnetic head slider and one bearing pad (trailing pad) disposed near the trailing side of the bearing surface.
JP-A-4-113568 discloses a magnetic disc drive using a liquid bearing in which four bearing pads are provided for the liquid bearing surface such that two of them are disposed near the leading side of the bearing surface and the remaining two are disposed near the trailing side of the bearing surface.
U.S. Pat. No. 5,202,803 discloses a magnetic head slider having two bearing surface pads disposed near the leading side of the air bearing surface and one bearing surface pad disposed near the trailing side. JP-A-5-54578, as mentioned above, discloses a magnetic head slider having a single bearig surface pad formed on the liquid bearing surface.
In JP-A-6-12808, it is proposed to use air bearing and liquid bearing in combination. In this case, two leading pads among three bearing surface pads are provided for air bearing and the remaining trailing pad is provided for liquid bearing.
In magnetic disc drives in which one to three bearing pads are provided for liquid bearing, however, jumping of the magnetic head slider cannot be avoided, because the attractive force of the liquid for attracting the bearing pads to the magnetic disc is weak.
In the magnetic disc drive disclosed in JP-A-4-113568, four bearing pads are provided for the liquid bearing such that two of them are disposed near the leading side of the bearing surface and the remaining two are disposed near the trailing side. The four pads, however, cannot contact the surface of the magnetic disc at the same time. Accordingly, jumping of the magnetic head cannot be also avoided by this configuration.